Vegetation cutting devices such as string trimmers are known power operated tools for cutting grass and other foliage and vegetation. Typically string trimmers are powered by petrol or electricity and an engine or motor drives a cutting head. The cutting head can comprise one or more rotating blades, in which case the trimmer is generally known as a brush cutter or one or more rotating lines, in which case it is known as a string trimmer. Many types of vegetation cutting devices, such as string trimmers employ a mechanism for allowing the user of the string trimmer to operate the string trimmer in a horizontal or “trimming” mode and in a vertical or “edging” mode.
When the string trimmer is in a trimming or horizontal mode, the plane of rotation of the cutting head and the cutting line is in a plane which is generally parallel with the ground. This means that the plane of rotation of the cutting lines is in an orientation for trimming grass or other vegetation. Typically grass growing in a lawn can be cut when the string trimmer is in the trimming mode.
In contrast when the string trimmer is in an edging mode, the plane of rotation of the cutting head is in a plane which is generally perpendicular to the ground. This means that the plane of rotation of the cutting lines are in an orientation which is suitable for cutting a line in vegetation. Typically grass at the edge of a lawn growing into a flowerbed can be cut when the string trimmer is in edging mode.
As with most vegetation cutting devices, string trimmers are susceptible to generating substantial noise when in use. The noise generated by a string trimmer in use comes mainly from the cutting line cutting vegetation and the cutting line passing through the air. The amount of noise will depend on a number of characteristics of the string trimmer, such as how fast the cutting lines are rotating, how thick the cutting line is, the length of the cutting line, and the shape of the cutting line. Typically, the greater the volume of air that the cutting line passes through in a unit time, the greater the level noise generated by the string trimmer in use.
The user can also affect the noise level generated by the string trimmer depending on how they use the string trimmer. For example a user attempting to cut dense vegetation may experience more noise than simply trimming the lawn. The orientation of the string trimmer will also affect the level of noise experienced by the user. For example a user can orientate the string trimmer in different positions and also modify the cutting head to cut in trimming or edging modes.
Personal protective equipment such as ear defenders can be used by the user to reduce the noise and prevent damage to the hearing of the user with prolonged use of the string trimmer. However ear defenders are unsightly and cumbersome and many users do not want to wear ear defenders when using a string trimmer. Furthermore a user may even forget to wear ear defenders until they are in the middle of the garden using the string trimmer at which point they cannot be bothered to fetch them.
In order protect the hearing of the user of the string trimmer, known string trimmers are configured to generate a maximum level of noise which does not exceed a certain limit. Typically the limit is determined to be such a level as not to cause damage to the user's hearing. For example the type of line used and the operational speed of the motor may be fixed and the user may not be able to vary these during operation. However in some instances the user may want more flexibility when using the string trimmer.
It is known to vary the speed of the motor of a string trimmer. In some circumstances a speed control dial can be used on a string trimmer. This means that a user can select what speed the motor should operate in. This means that the user can reduce the motor speed to economise power consumption. This can be particularly useful if the string trimmer is a cordless variety because the user can prolong the runtime of the string trimmer on a single battery charge.
DE 29819468 shows an example of a grass trimmer for use in a horizontal mode or vertical mode. In vertical mode the grass trimmer can be used for cleaning crevices. The speed of the string trimmer motor is determined by an electronic speed controller in the grip. This means the user can select the speed of the motor and reduce the speed of the motor when the string trimmer is operated in the vertical mode so stones and the like are less likely to be ejected from the crevices at high speed.
The user can decide to use the aforementioned vegetation cutting devices at a maximum motor speed at any point. Accordingly the vegetation cutting devices are designed to limit the noise generated by the line when rotated at the maximum motor speed for all types of operation.
A vegetation cutting device providing more flexibility for the user during use whilst managing noise levels which are experienced by the user is desirable. Embodiments of the present invention aim to address the aforementioned problems.